i6o BOTANICAL GAZETTE [February 



are absent, the fertile hyphae are uniformly isodiametric. It is 

 not certain whether these structures appear in all sporogenous 

 branches at some time preceding the contraction of the deHmited 

 protoplasts, or are more or less accidental in their occurrence. 

 They also are found associated with septa in the sterile axial fila- 

 ments, and here similarly occupy local hyphal distensions. After 

 the individual spores have become separated, the connecting seg- 

 ments of evacuated hyphal wall contract shghtly to form somewhat 

 narrowed isthmuses, which persist until the mature spore chains 

 are disrupted. In germinating, the spore usually produces i or 2 

 germ tubes. 



The preparation from which figs. 92-101 were drawn was derived 

 from one of 5 organisms communicated by Mr. M. Shapavalov, 

 who writes that "all were tested in inoculation experiments in 

 1912-1913, and proved to be pathogenic." Three of the other 

 organisms were found to be identical morphologically with the one 

 figured in plate VIII, while the fifth did not produce an aerial 

 mycelium sufficiently profuse to permit of a satisfactory microscopic 

 examination, although the general appearance of the culture indi- 

 cated that it also is identical with Actinomyces XVI. 



ACTINOMYCES XVIII 



Cultural characters. — On glucose agar, growth meager; 

 nutritive mycelium colorless; aerial mycelium slow to develop, 

 first white, later showing slight discoloration; diftusible pigment 

 absent. On potato agar, development very rapid; nutritive 

 mycelium dark; aerial mycelium profuse, felty, bluish gray; 

 guttation moderate; tyrosinase reaction vigorous. 



Morphology. — This species is characterized by an unusual 

 degree of variabihty in its fructifications. In figs. 102 and 107 is 

 represented a relationship between axial filament and sporogenous 

 branches common to many members of the genus. Fig. 108 shows 

 a slight departure from this type in the thickening of the subter- 

 minal portion of the axial filament bearing the spiral branches. 

 Further departures are expressed in the tufted grouping of the 

 spiral hyphae in fig. 104, and in the distended and extremely 

 vacuolated condition of the axial filament in fig. 106. A strikingly 



